This invention relates to mineral cutter picks and to assemblies of such picks with holding devices, for purposes such as breaking and excavating and having applications in mining, construction and civil engineering apparatus such as coal cutting machines.
Typically, a mineral cutter pick has a rearwardly projecting shank that is inserted into a correspondingly shaped aperture in its holding device in the manner of a spigot and socket connection. Locking means act between the pick and the holding device to retain the shank in the aperture during use.
As an example, in British Pat. No. 1,104,924 a cutter pick has a rectangular cross-section shank with a tapered outer portion that is drawn into engagement with the correspondingly tapered walls of the pick box slot by a locking pin. This construction has the disadvantage that an awkward and time-consuming machining operation is required to form the pick box slot so as to achieve the taper fit with the pick shank. In other known constructions, a constant cross-section shank and socket connection is used even though the manufacturing tolerances demanded for economic manufacture leave substantial paths for foreign material to penetrate into the connection. In the hostile environment of mineral cutting operations, rapid wear can result from the relative movement of the shank in the socket, accelerated by the presence there of foreign matter. In the examples of British Pat. No. 1,604,667 and No. 2,055,434 a shoulder is provided at the outer end of the shank for abutment against the outer face of the holding device surrounding the aperture. In such an arrangement the shoulder may go some way to shielding the aperture but it cannot exclude all foreign material. The movements that occur between the pick shank and its receiving aperture because of the slack fit between them still take place and the inevitable impress of foreign matter accentuates the adverse effects of these movements.